The invention relates in general to sensors and more specifically to flow rate sensors.
There are many situations in which it may be helpful to be able to detect and measure extremely small flow rates. For example, sensitive electronic products are often packaged, shipped, and stored in hermetically sealed electronic packages, where a leakage of minute amounts of oxygen and water vapor into the package will damage the circuitry. Similarly, even small volume changes in sealed chemical reaction vessels must be detected (e.g., by measuring extremely small flow rates into or out of the reaction vessels). There may be additional situations that also require the detection of extremely small flow rates and for which currently available methods are not effectual.
For example, the flow rate of a fluid can be measured by many methods, including deflection of a vane or a ball disposed in a fluid stream, rotation of a propeller, or the cooling effect of the fluid stream on a heated wire. However, these techniques are not effectual for measuring very tiny flow rates on the order of less than 1 picoliter per second.